Convert markdownlint library to an ECMAScript module, replace markdownlint-micromark with micromark, stop publishing (large) markdownlint-browser.js, see https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c for guidance.

lib/md045.mjs

@@ -0,0 +1,59 @@
+// @ts-check
+
+import { addError, getHtmlAttributeRe, nextLinesRe } from "../helpers/helpers.cjs";
+import { getHtmlTagInfo, getDescendantsByType } from "../helpers/micromark-helpers.cjs";
+import { filterByTypesCached } from "./cache.mjs";
+
+const altRe = getHtmlAttributeRe("alt");
+
+/** @type {import("./markdownlint.mjs").Rule} */
+export default {
+  "names": [ "MD045", "no-alt-text" ],
+  "description": "Images should have alternate text (alt text)",
+  "tags": [ "accessibility", "images" ],
+  "parser": "micromark",
+  "function": function MD045(params, onError) {
+    // Process Markdown images
+    const images = filterByTypesCached([ "image" ]);
+    for (const image of images) {
+      const labelTexts = getDescendantsByType(image, [ "label", "labelText" ]);
+      if (labelTexts.some((labelText) => labelText.text.length === 0)) {
+        const range = (image.startLine === image.endLine) ?
+          [ image.startColumn, image.endColumn - image.startColumn ] :
+          undefined;
+        addError(
+          onError,
+          image.startLine,
+          undefined,
+          undefined,
+          range
+        );
+      }
+    }
+
+    // Process HTML images
+    const htmlTexts = filterByTypesCached([ "htmlText" ], true);
+    for (const htmlText of htmlTexts) {
+      const { startColumn, startLine, text } = htmlText;
+      const htmlTagInfo = getHtmlTagInfo(htmlText);
+      if (
+        htmlTagInfo &&
+        !htmlTagInfo.close &&
+        (htmlTagInfo.name.toLowerCase() === "img") &&
+        !altRe.test(text)
+      ) {
+        const range = [
+          startColumn,
+          text.replace(nextLinesRe, "").length
+        ];
+        addError(
+          onError,
+          startLine,
+          undefined,
+          undefined,
+          range
+        );
+      }
+    }
+  }
+};